Seismograph recording apparatus



May 4, 1948. E. M. PALMER SEISNOGRAPH RECORDING APPARATUS Original FiledJune 14, 1945 6 Sheets-Sheet l ELTON M. PALM/ R I ATTORNEY May 4, 1948.E. M. PALMER ,970

SEISIIOGRAPH RECORDING APPARATUS Original Filed June 14, 1945 6Sheets-Sheet 2 v I 34 4O I 35 KO l 11 i 4 a A. 22 F v a5 v #33 1 19 a218 JO.

ELT N M. PALMER ATTORNEYv 4, 1948. I E. M. PALMER 2,440,970

SEISIOGRAPH RECORDING ABPARAIUS Original Filed June 14, 19 45 6Sheets-Sheet 3 10 TO DETECTOR TO DLETgcTo 516mm. CHANNEL NAL flFmNELFIRST mvuvms I REFLECTIONS lo L a u u D a PRIOR AR;-

-RODS DS ON Roms ON PART 32 PART 31 PART4O 3mm -LTOLN M. PALMER AATTORNEY May 4, 1948. E. M. PALMER 0 SEISMOGRAPH RECORDING APPARATUSOriginal Filed June 14, 1945 6 Sheets-Sheet 4 SHOT :iawunm 45 I PRIORiRTELT N M. PALMER ATTORNEY May 4, 1948. E. M. PALMER 2,440,970

sx-IsnoGRAPH RECORDING APPARATUS Original Filed June 14, 1945 6Sheets-Sheet 5 1 s A F R T R'RIVAl- REFLECTIONS 10 O G U 5 B 0 B U D B 15 5.73 i P M PRIOR :RRT M I iws RODS O'N-"RODS ON- PARTSI PART 40 7 160TO DETBCTOR BELT ON M. "PRLMER a, ATTORNEY Patented May 4, 19482,440,910 I smsmocmn arcoanmc arrana'rus Elton M. Palmer, Oakmont, Pa.,assignor to Gulf Research & Development Company, Pittsburgh, Pa., acorporation of Delaware Original application June 14, 1945, Serial No.599,337. Divided and this application January 15, 1948, Serial No. 2,530

2 Claims. 1

This invention relates to improvements in 8.! paratus for recordingseismic waves in seismograph prospecting. More particularly. it concernsapparatus for multi-channel seismic recording which produces a recorddevoid of angularity.

The instant application is a division of my copending application,Serial No. 599,337, filed June 14, 1945, entitled Seismograph recording.apparatus.

In seismograph prospecting, artificial earth tremors are created byfiring a charge of explosive in the earth, and seismic waves aredetected at a plurality of points spaced various distances from theexplosion or shot point. The detected tremors are commonly amplified andrecorded on a moving tape together with the instant of shock initiationand time increments. The seismic waves propagated from the source arereflected and refracted in subterranean strata and in particular at theinterfaces thereof, and from a study of the recordings inferences can bedrawn as to the depth, dip, etc., of subterranean strata.

The seismograph records usually take the form of a film or paper bandbearing a plurality of parallel record traces of the vibrations aspicked up at the several detectors. Each trace shows an initial impulsewhich is the so-called first arrival, followed by a series ofreflections. The reflections manifest themselves on the traces as moreor less the same series of events which are characteristic wave trainscoming from strata at various depths. The events are displaced withrespect to each other in time on the diiferent traces. An analysis ofthe traces is made to determine the attitude of underlying geologicalstrata, particularly their depth and dip. Variations in depth caused bydip or by faulting are revealed by time diflerences of correspondingevents on various correlated traces and records.

In the recordings, however, there are large differences in time whicharise, not from geological dip or faulting, but from the geometry of thefield setup. Some of the displacement of reflected events from trace totrace is due to the varying slant of the several wave paths; the part ofthe displacement due to the latter cause is commonly termed angularity.Consider two waves, one refiected from a shallow stratum and the otherfrom a deep stratum, and two detectors, one near and the other far fromthe shot point. The wave paths of reflections from the two strata to thenear detector are nearly the same as the vertical distances from thedetector to the strata (down and up) angularity for the wave paths fromeach stratum is small. For the far detector, the wave paths are muchlonger than the vertical di tances; angularity for these paths isrelatively large, and is larger for the shallow stratum than for thedeep stratum. The net result is that, particularly in the early part ofa record, similar events picked upby the near and far detectors arewidely displaced on the record tape and correlation may thereby be madedifficult. The angularity displacements gradually decrease in magnitudeas reflected waves from deeper strata are received toward the later partof the record.

By employing the apparatus of my invention, the time displacement ofcorresponding events due to angularity is eliminated so that whatremains is the part due to geological variation of the strata, that is,extraneous displacements are removed in making the record, leaving onlythose which are of geological interest. These considerations will beclear in the more detailed analysis given below.

Direct visual inspection of seismograph records gives useful qualitativeinformation before quantitative measurements are made. Certaincharacteristic fluctuations in the traces can be matched from record torecord and tentatively correlated. In the heretofore usual recordshaving angularity as above described, the usefulness of the record forpurposes of correlation is somewhat impaired because as stated, in thefirst part of the record especially, corresponding events areconsiderably displaced in time along the length of the record. Thedisplacement can be made somewhat less objectionable by running therecording fllm slower, that is, longitudinally compressing the record,or by spacing the several traces far apart laterally, but theseexpedients are not corrective and they are attended with disadvantages.

It is an object of this invention to provide apparatus for recordingseismic tremors received at a number of spaced points in such a way thatthe time displacements between traces of corresponding events are devoidof angularity on the resulting record.

Another object of the present invention is to produce a record of aplurality of series of similar seismic wave events, in which similarevents appear aligned across the record with respect to each other,except for displacements due to actual underground geologicalconditions, to facilitate visual comparison.

A further object of this invention is to provide recording apparatus foruse in seismograph prospecting which produces a record on which thegeological information sought is forcefully brought out withoutinterferences of extraneous time diflerences due to angularity.

These and other objects are achieved by autorection;

3 matically removing the angularity correction from the record duringthe recording process by the means herein described. The apparatus maybe more fully understood by reference to the drawings in which:

Fig. 1 is a diagram illustrative of the origin of angularitydisplacements;

Fig. 2 is an isometric view of one embodiment of my invention, utilizinga single cam surface;

Fig. 3 is a plan view corresponding to Fig. 1, to a reduced scale;

Fig. 4 is a schematic reproduction of an uncorrected record of the typeproduced by the devices of the prior art;

' Fig. 5 is a schematic reproduction of a corresponding record obtainedwith the aid of the apparatus of Figs. 2 and 3, or of Figs. 8 and 9;

Fig, 6 is a schematic representation of a group of records as recordedwithout angularity cor- Fig. 7 shows a corresponding group of recordsobtained with the aid of the apparatus of Figs. 2 and 3 or of Figs.8'and 9? Fig. 8 is a view in elevation of a modification utilizingspiral cams;

Fig. 9 is a view in plan of the apparatus of Fig. 8;

Fig. 10 is an isometric view of the apparatus of Figs. 2 and 3 adaptedto be used for pen recording elements;

Fig. 11 is a plan view corresponding to Fig. 10 to a reduced scale;

Fig. 12 is a view of a modification of Fig, 9 utilizing spiral cams andpen recording elements;

Fig. 13 is a schematic representation of an uncorrected variableamplitude record of the type produced by the devices of the prior art;

Fig. 14 is a schematic reproduction of a corresponding record obtainedby means of the apparatus of Figs. 10, 11, 12 or 15;

Fig. 15 is a plan view of the apparatus of Figs. 2 and 3 adapted to beused for optical oscillograph recording;

Fig. 16 is a chart illustrative of the manner of determining the shapesof the cams in the apparatus of Fig. 8; and

Fig. 17 is a diagram illustrative of certain principles on which theinvention is based.

Referring to the drawings, Fig. 1 illustrates angularity, as the term isused in the seismograph prospecting art, and shows why it varies withdetector distance and depth or time. As shown, a series of detectorsI00, IOI, I02, I03 and I04 are set up in the earth at differentdistances X from a shot point S. The detectors are connected toindividual amplifiers I05, I06, I01, I 08 and I09 which deliver torecording devices IIO heretofore in a straight line, adapted to make arecord on a traveling band I0. The recording devices I I0 may be of anyknown type, such as electrically driven recording pens, galvanometers,variable density recording lamps, or electromechanical orelectro-optical devices of any known kind.

On firing the shot, and considering the nearest and farthest detectorsI00 and I04, reflected waves which originate at shot S are picked up atdetectors I00 and I04 and recorded. Since these detectors are spacedfrom the shot, the wave paths are twice the length of diagonals a, b andc, which are longer than twice the corresponding vertical distances hi,ha and he. The consequent lag in arrival'times over the time for avertical path is said to be due to the angularity. Reflections frompoints H and J correspond to the same horizon but arrive at differenttimes. The angularity at detector I00 is very small since path a is veryslightly longer than hi. Path 1), however, is much longer than hz,resulting in greater angularity correction. Thus it can be seen that fora given reflecting horizon the angularity correction increases withdetector spacing so that the arrivals do not fall straight across therecord. As waves are received from deeper and deeper horizons, theangularit corrections decrease as can be seen by comparing the paths topoints J and K. Path 0 differs from h: by an amount smaller than thedifference between I) and k2. Thus the later reflections on aseismograph record fall more nearly on a straight line perpendicular tothe edges of the record.

In analyzing or interpreting a record whose traces represent the tremorspicked up at a series of detectors such as I00, IOI, I02, I03, I04, orin interpreting a series of such records taken with adjacent setups ofdetectors and shot points, one may look for the reflectioncharacteristic of a particular stratum as a characteristic impulse whichpersists across each setup. The unique identification of such an impulseis interfered with by the large angularity displacementsof the impulse.Such angularity is removed by my in- I vention thus permitting moredefinite identification of reflection impulses and facilitating theaccurate geological interpretation thereof.

Figs. 2 and 3 illustrate a preferred embodiment of my invention forcorrecting angularity. It is shown incorporated in a variable densityrecorder of the type making use of a plurality of lamps I2, Fig. 3, eachof which is connected to a seismograph detector signal channel in suchmanner that the lamp fiuctuates in brightness according to instantaneoussignal amplitude. The lamps are disposed adjacent a sensitive film orpaper band I 0, which is moved at a predetermined rate during therecording operation. The lamps are not shown in Fig. 2 in order toimprove clarity of the figure. A set of strips I4 is provided, eachhaving a slit I5 for one of the lamps I2, disposed over apertures I6,Fig. 2, in a stationary lightshield I! as shown, and mounted on rods I8guided for sliding movement in a support I9. Each rod has a channeledfoot 20 engaging the ends of another set of push rods 2I sliding inguides 22 which are mounted with the aid of nuts 23 in a slotted support24. Springs 25 are in compression and urge rods I8 in the directionshown.

Opposed to the opposite ends of rods 2 I is a cam 30. The cam has aplane portion 3|. Plane portion 3| of the cam gives way to two inclinedsurfaces 40 of such slope that for a given linear speed ratio betweenthe sliding cam 30 and film I0 slit members I4 will move slowly to theright while rods 2| are sliding down portions 40, movement of the slitsfaster than film I0 preferably being avoided. Following the inclinedsurfaces 40 the cam has a curved portion 32, the surface of which isthat of a circular c0ne,.the apex 33 of which lies in the plane, nearthe end of the cam. One element of the cone, 35--35, lies in the plane3| of the cam face along the central longitudinal axis thereof. The axisof the cone indicated by II0I'I0 is perpendicular to the plane of theslits; see Fig. 2. In order to more easily visualize the cone, its baseis sketched in Fig. 2 as the line "I. In the side elevation view, Fig.3, the axis of the cone is indicated by the line marked "0 and the baseby line III, and the element which lies in the plane 3| is shown as line35. The cam is mounted in sliding relation on a fixed guide 34 formovement along the direction of element 35-35. The cam is driven inpositive speed relation to the film through the agency of asprocket-and-chain connection 36 between a roller 31 over which the filmpasses, and a pinion 38 driving a rack 39 on the cam. A clutch II isprovided so that the cam mechanism may be engaged at the desired timeand disengaged in order to be reset for the next shot. The clutch ll maybe electromagnetically controlled.

Fig. 3 shows the apparatus at the beginning of its cycle of operationwith the rods 2| on the plane part 3| of the cam while Fig. 2 shows itnear the end of its cycle with the rods 2| on the conical curved part ofthe cam.

In operation, the apparatus is initially set to the position indicatedin Fig. 3. The film is set in motion somewhat prior to firing theexplosive which initiates the seismic waves. The correcting cammechanism is set in motion simultaneously with the shot by engagingclutch I I (Fig.

2). Alternatively the shot may be fired automatically and clutch llautomatically engaged at the same moment by operation of knowncoordinating switches and safety devices usually employed. While thefirst arrivals are being received, rods 2! are on plane portion 3| ofthe cam and the slits are in vertical alignment. Recording of thesefirst arrivals and also of subsequent impulses is effected by applyingthe amplified seismic detector signal to lamps I2 (see Fig. 3, the lampshave been omitted from Fig. 2 for clarity as previously stated) mountedon the strips H, as shown in Fig. 3. The lamps l2 fluctuate inbrightness according to the instantaneous signal amplitude and the lightof 'each lamp shines through its associated slit l5 onto thephotographic film [0. Thus the periodic detector signals are recorded onthe photographic film in the form of variable density tracks. Thus thefirst arrivals are recorded in displaced relation to each other. Shortlythereafter rods 2| move over surfaces 40 and on to the conical portion32 of the cam, so that when the reflected events come in, the slits aredisposed along a curve such as to bring the traces in vertical alignmentif no geological anomaly is present, or exhibiting only such.misalignment which may be ascribed to geological conditions.

Fig. 5 shows a record as obtained with the apparatus of Fig. 2 (assuminglevel strata) and Fig. 4 shows an ordinary uncorrected record of thesame events. The effective curvature of the cam progressively decreasesand the trace displacement becomes less and less.

Figs. 6 and 7 illustrate one of the chief objects of the invention as itapplies to visual use of seismograph records described above. Thevariable density records shown in Figs. 6 and 7 are a succession oflight and dark regions on a relatively narrow band, a very dark regionresulting from a large instantaneous signal in one direction and a verylight region resulting from a very large signal in the other direction.Such recordings possess the advantage that the received tremors appearas distinct markings on a band sufficiently narrow to be placed closetogether and various density traces or tracks may be recorded closelyadjacent to each other. In a group of such bands each made from adetector station, the relative values of Various events are easilydiscerned. One may place side by side, as in Figs. 6 and 7, a number ofsuch recordings, all made withthe same time scale and obtain amosaic-like array of light and dark bands which is essentially a timeplot of received events. Such a time plot is traversed by light and darkregions which persist from track to track as stripes, and since each isthe result of energy reflection from an underground geological stratum,one has in effect a shaded graph which pictures a cross section of theearth. The easily comprehended variable density traces give a strongvisual representation of the seismic events. The figures representschematically a group of variable density records I!) which might beobtained from a series of shot points and detectors arranged in aconventional straight line. These records are shown placed injuxtaposition, corresponding to the arrangement of the seismographapparatus on the earths surface, for the purpose of delineating the dipand depth of various subsurface strata. The seismic events in the recordarrangement shown give a qualitative picture of the relations betweencertain strata through a vertical plane or cross-section. Certain of theevents, which have been exaggerated in boldness in the sketches, show aconsistent alignment across each record and from record to record. Inseismograph interpretation practice, events occurring with suchalignments are considered as evidence of the presence of reflectingstrata and from them the dip and depth of the strata are computed. It isevident that many random alignments oflimited extent will in general beobservable and will be readily confused with the useful alignments whichmust be consistently traced over reasonably large extends. Thus it isdesirable ot remove, insofar as possible, the factors tending to confusethe proper correlation of seismic events.

Fig. 6 illustrates the way in which the angularity effect tends toconfuse the interpretation of a group of records made in the heretoforeconventional manner of the prior art. Reflection impulses I20 show awavy appearance due to angularity misalignment which makes the horizondifficult to follow. It often leads the interpreter to jump a wave cyclein his correlation, resulting in erroneous geological interpretation. K

Fig. 7 illustrates a similar set of records from which the angularityhas been removed in the recording process, as by the agency of theapparatus of Figs. 2 and 3. Fig. 7 shows how a group of records made bymeans of this invention resolve the reflection impulses into clear-cutalignments. Interpretation of groups of such records is clearlyfacilitated by the improved clarity of seismic event correlation.

In modern reflection seismograph prospecting practice, detectors areoften placed on both sides of the shot, and the apparatus of Figs. 2 and3 is shown in a form for correcting angularit in detecting waves on bothsides of the shot. If all the detectors are on one side only of theshot, the several rods 2| will be disposed all on one side of line 3535.In the figures only a few slits and actuators therefor are shown, forclarity. In working embodiments a larger number of slits is provided,corresponding to the relatively large number of detectors at presentused for each shot. The spacing of rods 2|, Fig, 2, in the slots ofsupport 24 is proportional to the spacing of detector stations, and maybe adjusted if desired by loosening nuts 23 and sliding guides 22 in theslot of support 24.

Figs. 8 and 9 show a modification of the invention making use of aplurality of spiral cams,

In the apparatus of Figs. 8 and 9 a plurality of 7 strips I4 havingslits-I5 are mounted on rods I40 guided in guides M on a light shield 42which is provided with apertures 43. A set of lamps l2 are provided overthe slits, each connected to a seismograph amplifier 44 and detector 45in a known manner such that the lamp fluctuates in intensity above thebelow a median value in accordance with instantaneous signal strength,thereby producing traces on a film I traveling over a roller 41.

The slits are controlled by a set of cams 50, 52,'of shape determined asdescribed below, fixed on a shaft 53 rotated at a definite angular speedwith respect to roller 41 through the agency of suitable gearing 54 andclutch 55. If, as is often the case, the detector corresponding to thetrace adjacent the edge of the film I0 is at the shot point, nocorrection is necessary, so the cam 50 may be a circle, or alternativelythe corresponding strip I4 may simply be fixed. The other cams havecircular portions, of the same radius as cam 50, which give way atpoints 56, 51 to inclined portions 58, 59, which in turn give way tospiral portions 60, 6|,beginning at points 62, 63. Springs I12preferably should be provided to keep sliders I40 against the cams, seeFig. 8. The cam shaft is initially set so that rods I40 rest at point Bon the circular part; that is, angle EQB=0. Point E represents thecontact point of the rod I40 on the cam, the center of the rotation ofthe cam being designated by Q. Point B is the starting point of the cam,that is the rods I40 initially contact the cams at point B. The angleEQB is therefore the angular travel of the cams and increases with timesince shaft 53 is driven from the film I0 through mechanical connection54. The film I0 is started just before the shot is fired, and clutch 55engaged at the shot moment, thus setting the cam shaft 53 into motion.Then the first arrivals are received with the slits ,in verticalalignment. The first arrivals remain displaced as in an ordinary record;see Figs. 4 and 5. Then each rod in turn slides down portions 58 and 59to points 52 and 53, in time to set the slits for maximum correctionduring receipt of the earliest reflected events. Thereafter the slitsgradually approach re-alignment again according to the required amountof correction. The correction usually becomes so small before point Bhas come back to its initial position that it may be eliminatedcompletely in the last few degrees of cam rotation.

Since therecord film I0 and the cams move at predetermined relativevelocities, each slit at any instant during the recording is displacedby an amount predetermined by the shape of the corresponding cam. As aresult of the control, the series of reflected wave events is recordedin the de- I sired vertical alignment shown in Fig. 5.

Following are the considerations governing the cam shapes of theapparatus of Figs. 8 and 9, and the curved surface 32 of Figs. 2 and 3.

The general formula for angularity correction A (in seconds) for anydetector located a distance a: from the shot point and receiving at timet after the shot an impulse reflected from a stratum at a depth h, isgiven by the following readily derived relations:

in which t is the observed travel time in seconds, t is the time inseconds for a pulse to travel from the shot point to a stratum at depthh and return to the shot point, a: is the shot-detector. distance andV11 is the average velocity to the stratum at depth h. The value of Vais customarily given in terms of h by a calibration chart based onempirical data. If h is assigned arbitrary values, the correspondingvalues for Vh will be found from the chart; and from the evidentrelation, Vnt'=2h, corresponding values for 1; may be obtained. Thus forgiven values of h and 2, correspondin values for A and t may be computedfrom ,the above formula.

If the recording paper speed is k inches per second, the displacement ofany slit i5 for any value of A must be kA inches. The angle a in radiansthrough which the cam (or cam shaft 53, Fig. 8) rotates in t seconds isa=wt, where w is the angular velocity in radians per second. Thus therequired displacement such as DE of Fig. 9 at all points around thecircumference of the cam are determined by corresponding values for aand kA, computed as described above from given values of h and :c. Theradius QE may have any.

convenient length.

For the purpose of subsequently computing weathering corrections, it isdesirable as mentioned above for the slits to be in line across therecord until after the first arrivals have been recorded. This requiresthe rods I40 to remain at the distance QE, Fig. 9, until a=wt1, where h,the first arrival time, equals the shot-detector distance divided by thevelocity in the bed through which the first arrival travels. Points 51and 56 correspond to first arrival times after which the slits areallowed to descend to the cam surfaces 60, 6| as computed above. Therate of displacement of the rods between points such as 51 and 63 shouldclosely equal but not exceed in inches per second since the slits shouldnot move faster than the recording paper.

Fig. 16 shows by way of a specific example two cam curves, computed fordetectors at 2000 feet and at 5000 feet from the shot point. Thevelocity V1 in the first arrival bed is taken as 3000 feet per second; arepresentative value. The data for Vn versus h were taken from a typicalfield calibration chart. The angular velocity w of the cam is taken as1/2 radians per second and the velocity of the recording paper isassumed to be such that the paper moves a distance Z in 0.01 second.Hence the distance indicated by Z along the radius in Fig. 16corresponds to an angularity correction of 0.01 second.

Again considering the apparatus of Figs. 2 and 3, this'embodiment isbased on the fact that the relation between the quantities A, t and:r/Va

where Vh in this case is a constant, may be written as the equation of acircle. Thus Equation 1 can be put in the form:

This equation in terms of time may be multiplied by k, in which it isthe velocity of the record, to convert it into terms of distances asfollows:

larity correction is kA. Fig. 17 indicates how the circle can be used tosupply corrections to record l through rods. In the simplest embodimentthe radius of the circle would be fixed and the correction would be goodonly at the one instant when its radius equals kt. If the radius is madeto vary directly with time to expand the circle as called for byEquation 3, the corrections will be appropriate throughout the length ofthe record.

The cone of Figs. 2 and 3 is a practical means The various rods shouldbe spaced from the point of tangency T by distances such as kx'IVh whichare proportional to the corresponding shot-de tector distances.

When the velocity Vh of seismic wave varies with depth, normallyincreasing with depth, the

compensation just described is approximate. However, the compensationcan be improved if desired by accelerating the cone in the latter partof the record; or the same effect can be achieved by maintaining uniformmotion and forming the cone surface with an appropriate bell-shapedflare towards the large end. Similarly, the shape of the cone may bemodified slightly to satisfy any particular conditions. The rods 2| inFig. 2 may also be moved closer together toward the end of the record;that is, by variably compressing with time the distances kx/Vh in Fig.1'7. Speeding up the cone or increasing its radius are less accurate butsimpler than moving the rods. Any residual error in the correctionsresulting from use of any of these expedients will be practicallynegligible. This is because the values of the angularity correction forwaves from deep strata, which in general are the ones exhibiting theincreased velocities, are in themselves very small (cf. Fig. 1 and thecorresponding description).

While I have illustrated my invention as applied to variable densityrecordings, the same may alternatively be used for other types ofrecordings. Conventional seismograms are frequently made by variableamplitude recording, the traces in this case being wavy lines whoseundulations correspond to the received earth tremors. In such recordingsit is of importance to avoid overlapping of traces. Large impulseshaving time displacement result in confusion or entanglement of traceswhich often defies analysis. Such large impulses are likely to occur inthe early part of the record when angularity displacements are alsogreater. However, if the time displacement is removed, all traces swingtogether in unison and thus keep out of each others way. Such an impulsewhen recorded without angularity as by my invention causes an otherwiseconfused tangle of traces to become resolved, revealing any alignmentwhich is the characteristic criterion of a reflection.

In the application of my apparatus to variable amplitude recording, thedevices H0 (Fig. 1) may be pen recording elements, such as well knownpiezo-electric crystal driven pen elements or electromagnetically drivenpen elements. Slits be mounted on arm 18 (Figs. 2 and 3) or I40 (Figs. 8and 9) eliminating parts l2, l4, l5, l6 and 11.

Figs. 10 and 11 show how such pen elements may be applied to theapparatus of Figs. 2 and 3. The pen elements 150 are mounted on arms 18,each movable pen arm l5l having a stylus resting on the record tape Ill.The pen element causes the stylus to move transversely in accordancewith the detector signals, and the cam mechanism similar to that ofFigs. 2 and 3, through the arm l8 moves the element longitudinally sothat reflected impulses will be recorded in time alignment on alltraces.

Fig. 12 shows how a pen element may be mounted on the apparatus of Figs.8 and 9 instead of using lamps and slits. In Fig. 12 the pen element I50carrying stylus l5l is mounted on arm I40 and its mode of operation issimilar to that in Figs. 10 and 11.

A similar arrangement may be provided when reflection galvanometer typeof oscillographs and photographic recording are used to obtain avariable amplitude trace, the optical system being arranged asillustrated in Fig. 15. In this v case the oscillographs 160 are usuallyplaced some I5 of Figs. 2 and 3 are not required when such distance fromthe photographic tape so as to obtain optical magnification of motion.The numerals in Fig. 15 refer to parts having similar function as partsbearing the same numeral in Fig. 3. The oscillograph element IE0 ismounted on arm 18 operated through parts 21 and 20 by the correctingcam. Also fastened to arm I8 is a light source Iil shielded by cover I62so that light is allowed to fall only on galvanometer mirror I53 whichis caused to oscillate by electromagnetic means about the longitudinalaxis, thus causing the light beam I64 to move transversely across tapeill in accordance with the received earth tremors. Action of theangularity correcting mechanism moves the beam longitudinally on thetape so as to bring reflected events into alignment as illustrated inFig. 14.

The resulting improved clarity obtained by means of my invention invariable amplitude recording is illustrated by Figs. 13 and 14, whichare similar to Figs. 4 and 5. Fig. 13 shows a simplified variableamplitude seismograph recording made in the heretofore conventionalmanner. Actual tapes are much more complicated and show even moreoverlapping of traces. One may observe that there is difliculty intracing the curves through the tangle of lines which occurs at theregion of large amplitude pulses. 0n the other hand Fig. 14 shows asimilar record made in the manner of this invention and in which theangularity is removed. One may readily note the simplification whichresults in improved clarity of the reflected events.

The apparatus of my invention may further be used in .the process ofre-recording of seismograms for purposes of special analysis. For suchpurposes it has been customary to originally make a variable densityrecord on transparent film. Other types of sound-on-film records mayalternatively be made. Such a record is easily reproducible by allowinga light source to shine light through a restricted area of the record onto a photocell. The photocell response may then be amplified andrecorded. Various useful operations may be performed on the photocellsignals such as filtering, differentiation, summing signals from varioustraces, etc.

If one has on hand a conventional seismo- "graph" EQQOiding of thereproducible type and having angularity displacements between events, myinvention may be used to obtain therefrom a recording of the 'sameevents having no angularity displacements, thereby achieving thesimplification of interpretation resulting from such recordings.Filtering, etc., may be simultaneously carried out during such recordingif desired. In such re-recording operations each of the elements H0,Fig. 1, is actuated by electrical signals coming from a photocell whoselight input is modulated by the corresponding trace of the originalrecording. These photocells are in space alignment so that their signalshave the same time sequence as the originally recorded events, while therecording elements H are moved in proper relationship by the agency ofmy apparatus. Thus the signals stated in the foregoing specification tobe derived from geophones or detectors may be derived from them in anindirect manner by the use of an intermediate recording of areproducible form. In such case the shaft will be connected throughsuitable gearing or through chain and sprocket to the mechanism whichdrives the intermediate record in the reproducing process, as well as tothe correcting apparatus shown connected through chain 38, Fig. 2. Myapparatus will then eliminate the angularity with a high degree ofprecision. Alternatively in the re-recording the apparatus may be usedto displace the photocells from alignment in the opposite sense andcause the angularity correction to be removed with equal precision.

What I claim as my invention is:

1. In a system for recording on a longitudinally moving record receivingband the seismic impulses from a seismic source received at a pluralityof distant seismic receiving stations by means of a plurality ofadjacent recording elements disposed to make contiguous records of 12seismic events received via electrical transmission channels from theirrespective seismic receiving stations, the improvement which comprisesmeans for independently longitudinally moving each of the recordingelements by a follower hearing on a moving cam surface, said cam surfacebeing in the form of a cone moved along an element thereof, each of saidfollowers being guided to move in a line at right angles to the axis ofsaid cone and at a lateral distance from said cone element which isproportional to the respective distance of the associated receivingstation from the seismic source, and means for moving said cam at aspeed proportional to the speed of the record receiving band.

2. In a system for recording on a longitudinally moving record receivingband the seismic impulses from a seismic source received at a pinralityof distant seismic receiving stations by means of a plurality ofadjacent recording elements disposed to make contiguous records ofseismic events received via electrical transmission channels from theirrespective seismic receiving stations, the improvement which comprisesmeans for independently longitudinally moving each of the recordingelements by a follower bearing on a moving cam surface, said cam surfacehaving such shape that progressive cross-sections thereof present acircular arc of continuously increasing radius, said followers beingguided so that their points of contact with the cam surface lie on acircular arc thereof, each point of contact being displaced a lateraldistance from the median plane of said cam which is proportional to thedistance of the associated receiving station from the seismic source,and means for moving said cam at a speed proportional to the speed ofthe record receiving band.

ELTON M. PALMER.

